The present invention relates to heat exchangers and in particular heat exchangers suitable for boiling a liquefied gas such as liquid oxygen in a reboiler/condenser of an air separation plant.
An effective way of transferring heat from the heated surface of a heat exchanger to a fluid in contact with the surface is through the mechanism of nucleate boiling. It has been found that if the heated surface is roughened the irregularities or cavities so formed, become nucleation sites for the formation of bubbles.
It is known to arrange for such bubbles to be pressed against the heated surface by means of a physical barrier which with the heated surface defines a narrow channel. An enlarged bubble area in contact with the heated surface results in a large percentage of the heated surface being covered by a thin microlayer of liquid from which evaporation takes place advantageously directly into the bubbles. However, as the bubbles progress along the channel the liquid is drained from the slugs between adjacent bubbles which can lead to a "dry-out" situation in which vapour is in contact with the heated surface, that is, evaporation to dryness.